diff --git a/src/alert.cpp b/src/alert.cpp
index eb1cd5e7f6ebe..9b79a3d62224c 100644
--- a/src/alert.cpp
+++ b/src/alert.cpp
@@ -121,7 +121,7 @@ bool CAlert::AppliesTo(int nVersion, const std::string& strSubVerIn) const
 
 bool CAlert::AppliesToMe() const
 {
-    return AppliesTo(PROTOCOL_VERSION, FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, std::vector<std::string>()));
+    return AppliesTo(PROTOCOL_VERSION, FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, std::vector<std::string>(), 0));
 }
 
 bool CAlert::RelayTo(CNode* pnode) const
diff --git a/src/clientversion.cpp b/src/clientversion.cpp
index aae0569bba211..9ab691668ed8e 100644
--- a/src/clientversion.cpp
+++ b/src/clientversion.cpp
@@ -7,6 +7,8 @@
 #include "tinyformat.h"
 
 #include <string>
+#include <iomanip>
+#include <cmath>
 
 /**
  * Name of client reported in the 'version' message. Report the same name
@@ -94,8 +96,18 @@ std::string FormatFullVersion()
 /** 
  * Format the subversion field according to BIP 14 spec (https://github.com/bitcoin/bips/blob/master/bip-0014.mediawiki) 
  */
-std::string FormatSubVersion(const std::string& name, int nClientVersion, const std::vector<std::string>& comments)
+std::string FormatSubVersion(const std::string& name, int nClientVersion, std::vector<std::string> comments, uint64_t nMaxBlockSize)
 {
+    if (nMaxBlockSize) {
+        // Announce our excessive block acceptence.
+        comments.insert(comments.end(), std::string("BIP100"));
+
+        std::stringstream ss;
+        double dMaxBlockSize = static_cast<double>(nMaxBlockSize) / 1000000;
+        ss << "EB" << std::setprecision(static_cast<int>(std::log10(dMaxBlockSize))+7) << dMaxBlockSize;
+        comments.insert(comments.end(), ss.str());
+    }
+
     std::ostringstream ss;
     ss << "/";
     ss << name << ":" << FormatVersion(nClientVersion);
diff --git a/src/clientversion.h b/src/clientversion.h
index ab79da9b36b87..b3b648d2ff04f 100644
--- a/src/clientversion.h
+++ b/src/clientversion.h
@@ -50,6 +50,7 @@
 
 #include <string>
 #include <vector>
+#include <stdint.h>
 
 static const int CLIENT_VERSION =
                            1000000 * CLIENT_VERSION_MAJOR
@@ -63,7 +64,7 @@ extern const std::string CLIENT_DATE;
 
 
 std::string FormatFullVersion();
-std::string FormatSubVersion(const std::string& name, int nClientVersion, const std::vector<std::string>& comments);
+std::string FormatSubVersion(const std::string& name, int nClientVersion, std::vector<std::string> comments, uint64_t nMaxBlockSize);
 
 #endif // WINDRES_PREPROC
 
diff --git a/src/init.cpp b/src/init.cpp
index 03cae603c2aba..35552f3b6ec1c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1139,17 +1139,17 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
     RegisterNodeSignals(GetNodeSignals());
 
     // sanitize comments per BIP-0014, format user agent and check total size
-    std::vector<string> uacomments;
     BOOST_FOREACH(string cmt, mapMultiArgs["-uacomment"])
     {
         if (cmt != SanitizeString(cmt, SAFE_CHARS_UA_COMMENT))
             return InitError(strprintf(_("User Agent comment (%s) contains unsafe characters."), cmt));
-        uacomments.push_back(SanitizeString(cmt, SAFE_CHARS_UA_COMMENT));
+        vUAComments.push_back(SanitizeString(cmt, SAFE_CHARS_UA_COMMENT));
     }
-    strSubVersion = FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, uacomments);
-    if (strSubVersion.size() > MAX_SUBVERSION_LENGTH) {
+    uint64_t hugeBlock = static_cast<uint64_t>((100000. / 3.) * MAX_BLOCK_SIZE);
+    size_t userAgentLen = FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, vUAComments, hugeBlock).size();
+    if (userAgentLen > MAX_SUBVERSION_LENGTH) {
         return InitError(strprintf(_("Total length of network version string (%i) exceeds maximum length (%i). Reduce the number or size of uacomments."),
-            strSubVersion.size(), MAX_SUBVERSION_LENGTH));
+            userAgentLen, MAX_SUBVERSION_LENGTH));
     }
 
     if (mapArgs.count("-onlynet")) {
diff --git a/src/main.cpp b/src/main.cpp
index eaa5ede611faa..e50a27e898b9e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -303,6 +303,12 @@ int GetHeight()
     return chainActive.Height();
 }
 
+int GetMaxBlockSize()
+{
+    LOCK(cs_main);
+    return chainActive.Tip()->nMaxBlockSize;
+}
+
 void UpdatePreferredDownload(CNode* node, CNodeState* state)
 {
     nPreferredDownload -= state->fPreferredDownload;
@@ -572,6 +578,7 @@ void RegisterNodeSignals(CNodeSignals& nodeSignals)
     nodeSignals.SendMessages.connect(&SendMessages);
     nodeSignals.InitializeNode.connect(&InitializeNode);
     nodeSignals.FinalizeNode.connect(&FinalizeNode);
+    nodeSignals.GetMaxBlockSize.connect(&GetMaxBlockSize);
 }
 
 void UnregisterNodeSignals(CNodeSignals& nodeSignals)
@@ -582,6 +589,7 @@ void UnregisterNodeSignals(CNodeSignals& nodeSignals)
     nodeSignals.SendMessages.disconnect(&SendMessages);
     nodeSignals.InitializeNode.disconnect(&InitializeNode);
     nodeSignals.FinalizeNode.disconnect(&FinalizeNode);
+    nodeSignals.GetMaxBlockSize.disconnect(&GetMaxBlockSize);
 }
 
 CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
@@ -4000,7 +4008,7 @@ bool LoadBlockIndex(bool* fRebuildRequired)
     return true;
 }
 
-bool InitBlockIndex(const CChainParams& chainparams) 
+bool InitBlockIndex(const CChainParams& chainparams)
 {
     LOCK(cs_main);
 
diff --git a/src/net.cpp b/src/net.cpp
index ae69a0c730bdd..319f148f60603 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -84,7 +84,7 @@ static std::vector<ListenSocket> vhListenSocket;
 CAddrMan addrman;
 int nMaxConnections = DEFAULT_MAX_PEER_CONNECTIONS;
 bool fAddressesInitialized = false;
-std::string strSubVersion;
+std::vector<std::string> vUAComments;
 
 vector<CNode*> vNodes;
 CCriticalSection cs_vNodes;
@@ -442,6 +442,7 @@ void CNode::CloseSocketDisconnect()
 void CNode::PushVersion()
 {
     int nBestHeight = g_signals.GetHeight().get_value_or(0);
+    int nMaxBlockSize = g_signals.GetMaxBlockSize().get_value_or(0);
 
     int64_t nTime = (fInbound ? GetAdjustedTime() : GetTime());
     CAddress addrYou = (addr.IsRoutable() && !IsProxy(addr) ? addr : CAddress(CService("0.0.0.0",0)));
@@ -451,6 +452,7 @@ void CNode::PushVersion()
         LogPrint("net", "send version message: version %d, blocks=%d, us=%s, them=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), addrYou.ToString(), id);
     else
         LogPrint("net", "send version message: version %d, blocks=%d, us=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), id);
+    std::string strSubVersion = FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, vUAComments, nMaxBlockSize);
     PushMessage(NetMsgType::VERSION, PROTOCOL_VERSION, nLocalServices, nTime, addrYou, addrMe,
                 nLocalHostNonce, strSubVersion, nBestHeight, !GetBoolArg("-blocksonly", DEFAULT_BLOCKSONLY));
 }
@@ -2580,14 +2582,14 @@ bool CBanDB::Read(banmap_t& banSet)
         // ... verify the network matches ours
         if (memcmp(pchMsgTmp, Params().MessageStart(), sizeof(pchMsgTmp)))
             return error("%s: Invalid network magic number", __func__);
-        
+
         // de-serialize address data into one CAddrMan object
         ssBanlist >> banSet;
     }
     catch (const std::exception& e) {
         return error("%s: Deserialize or I/O error - %s", __func__, e.what());
     }
-    
+
     return true;
 }
 
diff --git a/src/net.h b/src/net.h
index a6801690f462f..b0c3d6339a621 100644
--- a/src/net.h
+++ b/src/net.h
@@ -119,6 +119,7 @@ struct CNodeSignals
     boost::signals2::signal<bool (CNode*), CombinerAll> SendMessages;
     boost::signals2::signal<void (NodeId, const CNode*)> InitializeNode;
     boost::signals2::signal<void (NodeId)> FinalizeNode;
+    boost::signals2::signal<int ()> GetMaxBlockSize;
 };
 
 
@@ -174,8 +175,8 @@ extern CCriticalSection cs_vAddedNodes;
 extern NodeId nLastNodeId;
 extern CCriticalSection cs_nLastNodeId;
 
-/** Subversion as sent to the P2P network in `version` messages */
-extern std::string strSubVersion;
+/** Comments in subversion sent to the P2P network in `version` messages */
+extern std::vector<std::string> vUAComments;
 
 struct LocalServiceInfo {
     int nScore;
diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index b4ac69639304b..74784e18372fa 100644
--- a/src/qt/clientmodel.cpp
+++ b/src/qt/clientmodel.cpp
@@ -183,7 +183,7 @@ QString ClientModel::formatFullVersion() const
 
 QString ClientModel::formatSubVersion() const
 {
-    return QString::fromStdString(strSubVersion);
+    return QString::fromStdString(FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, vUAComments, 0));
 }
 
 QString ClientModel::formatBuildDate() const
diff --git a/src/rpcnet.cpp b/src/rpcnet.cpp
index 779e7fbc6aa25..22c13a5e2cec6 100644
--- a/src/rpcnet.cpp
+++ b/src/rpcnet.cpp
@@ -466,7 +466,8 @@ UniValue getnetworkinfo(const UniValue& params, bool fHelp)
 
     UniValue obj(UniValue::VOBJ);
     obj.push_back(Pair("version",       CLIENT_VERSION));
-    obj.push_back(Pair("subversion",    strSubVersion));
+    obj.push_back(Pair("subversion",
+        FormatSubVersion(CLIENT_NAME, CLIENT_VERSION, vUAComments, 0)));
     obj.push_back(Pair("protocolversion",PROTOCOL_VERSION));
     obj.push_back(Pair("localservices",       strprintf("%016x", nLocalServices)));
     obj.push_back(Pair("timeoffset",    GetTimeOffset()));
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index 517e6945cf9bc..4ecf97a6f0c5b 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -11,6 +11,7 @@
 #include "utilstrencodings.h"
 #include "utilmoneystr.h"
 #include "test/test_bitcoin.h"
+#include "consensus/consensus.h"
 
 #include <stdint.h>
 #include <vector>
@@ -419,9 +420,15 @@ BOOST_AUTO_TEST_CASE(test_FormatSubVersion)
     std::vector<std::string> comments2;
     comments2.push_back(std::string("comment1"));
     comments2.push_back(SanitizeString(std::string("Comment2; .,_?@-; !\"#$%&'()*+/<=>[]\\^`{|}~"), SAFE_CHARS_UA_COMMENT)); // Semicolon is discouraged but not forbidden by BIP-0014
-    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, std::vector<std::string>()),std::string("/Test:0.9.99/"));
-    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments),std::string("/Test:0.9.99(comment1)/"));
-    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments2),std::string("/Test:0.9.99(comment1; Comment2; .,_?@-; )/"));
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, std::vector<std::string>(), 0),std::string("/Test:0.9.99/"));
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments, 0),std::string("/Test:0.9.99(comment1)/"));
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments2, 0),std::string("/Test:0.9.99(comment1; Comment2; .,_?@-; )/"));
+
+    // BIP100
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, std::vector<std::string>(), MAX_BLOCK_SIZE),std::string("/Test:0.9.99(BIP100; EB1)/"));
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments, MAX_BLOCK_SIZE),std::string("/Test:0.9.99(comment1; BIP100; EB1)/"));
+    BOOST_CHECK_EQUAL(FormatSubVersion("Test", 99900, comments, MAX_BLOCK_SIZE + (MAX_BLOCK_SIZE / 3)),
+            std::string("/Test:0.9.99(comment1; BIP100; EB1.333333)/"));
 }
 
 BOOST_AUTO_TEST_CASE(test_ParseFixedPoint)